Our invention relates to electric lamps in general and, in particular, to electric lamp assemblies comprising a lamp or light bulb and a reflector. More particularly our invention deals with improved means for mounting the lamp in position on the reflector in such a lamp assembly. The improved means of our invention have particular utility in conjunction with sealed beam lamp assemblies, having an incandescent lamp such as a halogen lamp mounted within a molded-glass housing, suitable for use as automotive headlamps or headlights.
As is well known, the halogen lamp is a type of incandescent lamp utilizing a halogen regenerative cycle for the longer life of its filament or filaments. On the strengths of its greater durability and higher luminous efficacy the halogen lamp is finding ever-increasing use as the light sources of automotive headlamps and similar lighting installations. A problem occurs in such applications of the halogen lamp, however, because of the fact that the filaments of commercially available halogen lamps do not necessarily lie in correct positions within the lamp bulbs or envelopes.
Let us consider, as an illustration of the problem, a typical sealed beam hardlamp assembly in which a halogen lamp is mounted within an inert-gas-filled, molded-glass housing. The lamp housing comprises a reflector and a control-lens cover, which are sealed together after the lamp is mounted in position on the reflector. It has been known to mount the lamp on the reflector via a straight, metal-made support rod. Rigidly anchored at one end to one of the ferrules on the back of the reflector, and support rod extends forwardly from the reflector and has its front end spot-welded to a metal band tightly wrapped around the base of the lamp. The support rod serves also as an electrical connection between the ferrule and one of the lamp leads.
As has been mentioned, the filament or filaments of the halogen lamp may be displaced from the proper position relative to the bulb. In this case the correct positioning of the bulb itself on the reflector results in the misplacement of the filament or filaments relative to the reflector. The bulb must therefore be amounted suitably displaced on the reflector for the proper positioning of the filament or filaments.
The conventional practice to this end has been to bend the support rod in situ, usually at two different points in the middle of the rod. The following two methods have been known for bending the support rod:
1. The "cold bending" method in which the support rod is bent at room temperature.
2. The "hot bending" method in which the support rod is bent while being heated.
The cold bending method gives rise to springback, that is, the gradual return of the support rod to its original straight shape. Consequently the filament or filaments of the lamp supported by the support rod also undergo gradual displacement from the proper position relative to the reflector.
Such springback of the support rod will not occur if it is bent by the hot bending method. This process requires, however, the use of a heater devised exclusively for that purpose and involves a troublesome, time-consuming operation. Another known practice, alternative to the hot bending method, has been to bend the support rod through greater angles than are required for the proper positioning of the lamp filaments at the moment, to compensate for its springback. An objection to this practice is the difficulty of accurate compensation for springback.
Whichever method is employed, the bending of the support rod at two spaced midpoints thereon is subject to the additional objection that the support rod allows oscillations of the lamp about its bent points during the travel of the vehicle. Such complex oscillations or vibrations of the lamp result in the flickering of the beam thrown thereby, with the consequent danger of dazzling the drivers of oncoming vehicles.